Erlang audio server

[David Michael]

Hi All,

I tried to post this to the general Erlang Programming list without
much success, so I thought I would try it here.

I am looking to write an audio server that can respond to messages
from Erlang processes. My intent is that this would be more like an
instrument, rather than a media server. The library I would like to
use for the audio engine is in C or C++.

What is the best way to do this?
Port, C node, or linked-in driver?

Thanks in advance
David

[Mihai Balea]

If you intend to just control your audio server with erlang, then a
port would do it. If the audio server is to be run on a different
machine, then a C node.
Basically, if it doesn't require top performance, I'd stay away from
linked in drivers, since they can crash the entire VM.

Mihai

[Will Schenk]

I've some a couple little port problems with ruby and it's been super simple.

--
Will Schenk
http://www.sublimeguile.com

[David Michael]

In doing so, did you have to start the Ruby process first, or did it
not matter?

[Will Schenk]

start() ->
spawn( fun() ->
% register( parser, self() ),
process_flag( trap_exit, true ),
Cmd = "ruby parser.rb",
Port = open_port({spawn, Cmd}, [{packet, 4}, nouse_stdio,
exit_status, binary]),
port_loop(Port)
end).

and the parser.rb was

require 'rubygems'
require 'JSON'
require 'erlectricity'
require 'tvtorrent'

receive do |f|
f.when([:parse, String, String, String]) do |mod, user, pass|
case mod
when "tvtorrent"
f.send!([:result, TvTorrent.new( user, pass ).new_fav_torrents.to_json])
when "sleep"
STDERR.puts "Sleeping for #{user} seconds"
sleep user.to_i
f.send!([:result, "Done sleeping"])
else
f.send!([:result, "Unknown module type #{mod}"])
end

f.receive_loop
end
end

[David Michael]

Awesome.
I take it that Erlang is running the Ruby script dynamically then (no
'$ ./parser.rb' first)?

[Will Schenk]

Correct. I can send you the whole mess if you want, it does handle
the script blowing up I believe. I haven't looked at it in a while,
so maybeI'm making it up.

[David Michael]

Sure, I'd love to see the example if you can rip it out of the rest of
the codebase.
Sounds like a port is the right way to go for this since my audio
server need not run on another machine. Even if it did need to run on
another machine, it does not need to be addressable from anything
other than Erlang processes.

D

[Will Schenk]

Attached is parser.erl and parser_pool.erl. After you start them up,
you would check out a parser from the parser_pool which would maintain
up to I think it's 4 separate os-level processes. Then release them
and they are usable by your friends.

Have fun.